Gas Detectomg Element and Gas Detecting Device Suited for Same

ABSTRACT

A gas detecting element that can effectively prevent fluctuations in measurement sensitivity caused by diffusion of a reagent as well as the occurrence of corrosion. The gas detecting element comprises a frame  1  with an optical density detection window  4  that is not gas-permeable formed on one side to allow optical density detection, and a gas-permeable window  6  formed on the opposing side, with a reagent absorbent material  7  being housed between the two windows and impregnated with a reagent that undergoes coloration change by reaction with a gas to be measured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas detecting element that detectsthe concentration of a gas by coloration reaction, and a gas detectingdevice suited to the detecting element.

2. Description of Related Art

A typical gas detecting element that generates a reaction colorationwhen gas reacts with a carrier such as cellulose can reliably detectextremely low gas concentrations by extending the sampling time.However, since the carrier is normally formed in a tape shape that ishoused on a reel, a paper-feeding mechanism is required. Such aconstitution not only adds an additional level of complication to thestructure of the measuring device, but also leads to problems such asbreakage of the carrier during feeding due to degradation of the carriercaused by the reaction reagent being supported.

In order to solve the aforementioned problems, a gas detecting elementhas been proposed as disclosed in Japanese Unexamined PatentApplication, Publication No. 2003-139762. This gas detecting elementconsists of a reagent and a carrier to be impregnated therewith housedin a thin container as a cell separated by a breakable membrane.Breakage of the membrane during use causes the carrier to be impregnatedwith the reagent, thereby preparing the carrier to be used for gasconcentration measurement.

Such a constitution can effectively prevent degradation of the gasdetecting element prior to use, and also does not require apaper-feeding mechanism, which can reduce the size of the measuringdevice employing the cell.

However, the reaction reagent that impregnates the carrier can diffuseduring measurement and adhere to the measuring means that detects theoptical density of the carrier. This leads to disadvantages such aschanges in the detection sensitivity of the measuring means, and whenthe reagent contains acid, there is the risk of corrosion of themeasuring means.

SUMMARY OF THE INVENTION

The present invention was achieved in view of the above circumstancesand has as its object to provide a gas detecting element that canprevent fluctuations in sensitivity caused by diffusion of the reactionreagent and also inhibit corrosion.

Another object of the present invention is to provide a measuring devicethat is suited to the aforementioned gas detecting element.

The invention according to claim 1 for resolving the aforementionedproblems is a gas detecting element comprising a hollow container; anoptical density detection window that is not gas-permeable formed on oneside of said container to allow optical density detection; agas-permeable window formed on the opposing side of said container; anda reagent that exhibits coloration by reaction with a gas to be measuredhoused in a space between said windows.

In the invention according to claim 2, said optical density detectionwindow is constituted by affixing a transparent, non-permeable film to aframe that constitutes said container.

In the invention according to claim 3, said optical density detectionwindow is formed at the same time as injection molding of said containerwith a transparent, non-permeable material.

In the invention according to claim 4, a reagent absorbent materialimpregnated with said reagent is housed in said space.

In the invention according to claim 5, a light-reflective surface isformed on the side of said gas-permeable window facing said reagentabsorbent material.

The invention according to claim 6 is a gas detecting device comprisinga gas exposure portion that opens to a sampling flow path; and anoptical density measuring portion provided with a light-emitting meansfacing said exposure portion and light receiving means, wherein saidexposure portion and said optical density measuring portion areoppositely disposed in a separatable manner, and a gas detecting elementis housed so that a gas inflow side of the gas detecting element facesthe gas exposure portion and an optical density detection portion of thegas detecting element faces said optical density measuring portion.

In the invention according to claim 7, said optical density detectionportion and said gas detecting element are constituted so as to maintainairtightness.

EFFECTS OF THE INVENTION

The invention according to claim 1 can prevent a gas and a reactionreagent from flowing into an optical density detection portion throughan optical density detection window, and therefore can preventfluctuations in sensitivity caused by diffusion of the reaction reagentand inhibit corrosion.

The invention according to claim 2 allows the material constituting theoptical density detection window to be selected independently of thecontainer.

The invention according to claim 3 eliminates the labor of affixing afilm constituting the optical density detection window and can preventleakage of liquid due to defective adhesion.

The invention according to claim 4 can prevent leakage of the reagenteven when it is a liquid by retaining it in the reagent absorbentmaterial.

The invention according to claim 5 can detect the optical density of thereagent absorbent material at a high sensitivity by preventing the lightfrom the light-emitting means from being absorbed.

The invention according to claim 6 can detect optical density whileblocking the gas to be detected and the reagent by the non-permeabilityof the optical density detection window.

The invention according to claim 7 can prevent the gas to be detectedfrom flowing into the optical density measuring portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a cross-sectional view of the first embodiment of the gasdetecting element of the present invention, and FIG. 1(B) is an explodedperspective view of the same.

FIG. 2 is a cross-sectional view of one embodiment of the gas detectingdevice in the state of the gas detecting element set therein.

FIG. 3 is a cross-sectional view showing another embodiment of the gasdetecting element.

FIG. 4(A) is a cross-sectional view of the second embodiment of the gasdetecting element of the present invention, and FIG. 4(B) is an explodedperspective view of the same.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1(A) and (B) respectively show a cross-sectional view and anexploded perspective view of the first embodiment of a gas detectingelement of the present invention. A surface 2 on one side of aring-shaped frame 1 is sealed with a transparent or semi-transparentnon-permeable film 3, whereby an optical density detection window 4 isformed. A gas passage layer 6 is formed on another surface 5 on theother side of the frame 1. In a cell formed between the non-permeablefilm 3 and the gas passage layer 6 is housed a reagent absorbentmaterial 7 that is a porous material of a color density, preferablywhite, that enables detection of coloration change due to reaction of areagent. In the present embodiment, the reagent absorbent material 7 isa nonwoven fabric such as glass fiber.

The gas passage layer 6 is constituted of a material provided withcorrosive resistance and light reflectivity, with gas passage holes 6 aformed therethrough. The material constituting the gas passage layer 6may be a film comprising aluminum foil coated with a polymer material ora laminate film consisting of laminated polymer film. Changing the sizeand number of the gas passage holes 6 a can adjust the quantity of gasthat flows inside, and thereby alter the detection sensitivity.

The reagent absorbent material 7 is housed so as to adhere closely tothe film 3 of the optical density detection window 4 for optical densitydetection by a measuring device described below.

The nonwoven material constituting the reagent absorbent material 7 maybe impregnated with the reagent in advance before being housed, orimpregnated with the reagent after being housed in the cell bydelivering a specified amount of the reagent by drops through the gaspassage holes 6 a to soak into the material.

A frame 9 provided on the optical density detection window 4 has atapered portion 9 a for guiding the distal end of a measuring headdescribed below.

FIG. 2 shows one embodiment of the measuring device suited to theaforementioned gas detecting element 10. The measuring device comprisesan exposure portion 22 that has an opening 21 located in a flow path 20of the gas to be measured and a measuring head 23. The measuring head 23and the exposure portion 22 are constituted to be separatable from eachother.

A through-hole 24 that is perpendicular to the detection window 4 of thegas detecting element 10 and through-holes 25, 25 that are slanted so asto intersect at the end of the through-hole 24 are formed in themeasuring head 23. A light-receiving means 26 is housed in thethrough-hole 24 and light-emitting means 27, 27 are housed in thethrough-holes 25, 25.

A gas sealing member 28 such as a packing is disposed at the opening ofthe exposure portion 22 to facilitate an airtight engagement with thesurface of the gas detecting element 10. Also, providing an annularpacking on the surface of the measuring head 23 in contact with theouter periphery of the optical density detection window 4 can preventthe gas to be detected and the reagent from flowing into the measuringhead 23.

In the present embodiment, the optical density detection window 4 of thegas detecting element 10 is set so as to face downward, that is, to facethe measuring head 23, and is joined to the exposure portion 22 and themeasuring head 23. By drawing in the gas to be measured with a suctionpump, a portion of the gas to be measured flows into the opening 21, andtherefrom passes through the gas passage holes 6 a of the gas passagelayer 6 into the reagent absorbent material 7.

The reagent in the reagent absorbent material 7 then reacts with the gasto be measured to yield a coloring reaction. When a specified time haselapsed, the measuring head 23 is actuated to that light from thelight-emitting means 27, 27 is irradiated on the optical densitydetection window 4. The light emitted from the light-emitting means 27,27 is reflected by the reagent absorbent material 7 to an extentdepending on its optical density. By detecting the intensity of thereflected light with the light-receiving means 26, the concentration ofthe gas being measured can be found.

In the present embodiment, since the optical density detection window 4is disposed facing downward, the reagent absorbent material 7 adheresclosely to the film 3 of the optical density detection window 4. Thisenables reliable and accurate detection of changes in the opticaldensity of the reagent absorbent material 7.

By applying a reflective finish to the surface of the gas passage layer6 facing the reagent absorbent material 7, the optical density of thereagent absorbent material 7 can be reliably detected at a highsensitivity without the light from the light-emitting means 27, 27 beingabsorbed.

Since the opening of the measuring head 23 is sealed by the film 3 atthe optical density detection window 4 of the gas detecting element 10,the gas to be detected and volatile matter of the reagent are preventedfrom entering the measuring head 23. Consequently, there is no foggingand corrosion of the light-receiving means 26 and the light-emittingmeans 27, 27.

When the measurement is complete, the measuring head 23 is removed toallow replacement of the gas detecting element 10 for the nextmeasurement.

In the aforementioned embodiment, the gas passage layer 6 wasconstituted separately from the frame 1. However, as shown in FIG. 3, itwill be recognized by one skilled in the art that the same effect can beachieved by forming the frame 1 in a flat-bottomed, cylindrical shapewith gas passage holes 6 a allowing passage of the gas being formed in abottom portion 1 a thereof.

FIGS. 4(A) and (B) shows a second embodiment of the gas detectingelement, denoted by the reference numeral 10′. In this embodiment, aframe 1′ formed by injection molding of an optically-transparent polymermaterial, such as polyethylene, and a thin wall 2′ that serves as theoptical density detection window are integrally formed. A taperedportion 1 b′ is formed as appropriate on the inner circumferential faceof the end portion of the frame 1′.

In the present embodiment, the gas detecting element 10′ is constitutedwith the reagent absorbent material 7 loaded from an opening 1 a′ sideof the frame 1′, with the gas passage layer 6 affixed to the opening 1a′. Similarly to the first embodiment, the reagent absorbent material 7may be impregnated with the reagent in advance, or impregnated with thereagent after being housed.

The present embodiment does not require the transparent orsemi-transparent non-permeable film 3 as disclosed in the firstembodiment, and so eliminates the labor of affixing the film 3 to theframe with an adhesive or the like. As a result, leakage of liquid intothe detecting device due to defective adhesion of the film 3 can beprevented.

In the aforementioned embodiments, the reagent absorbent material ishoused in the space formed in the container and impregnated with areagent that is retained in the reagent absorbent material so as to notto leak out. However, the present invention is not limited thereto. Forexample, the reagent absorbent material may be eliminated by treatingthe reagent to be highly viscous or a paste.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. A gas detecting element comprising: a hollow container; an opticaldensity detection window that is not gas-permeable formed on one side ofsaid container to allow optical density detection; a gas-permeablewindow formed on the opposing side of said container; and a reagent thatexhibits coloration by reaction with a gas to be measured housed in aspace between said windows.
 2. A gas detecting element in accordancewith claim 1, wherein: said optical density detection window isconstituted by affixing a transparent, non-permeable film to a framethat constitutes said container.
 3. A gas detecting element inaccordance with claim 1, wherein: said optical density detection windowis formed at the same time as injection molding of said container with atransparent, non-permeable material.
 4. A gas detecting element inaccordance with claim 1, wherein: a reagent absorbent materialimpregnated with said reagent is housed in said space.
 5. A gasdetecting element in accordance with claim 1, wherein: alight-reflective surface is formed on the side of said gas-permeablewindow facing said reagent absorbent material.
 6. A gas detecting devicecomprising: a gas exposure portion that opens to a sampling flow path;and an optical density measuring portion provided with a light-emittingmeans facing said exposure portion and light receiving means, whereinsaid exposure portion and said optical density measuring portion areoppositely disposed in a separateable manner, and a gas detectingelement is housed so that a gas inflow side of the gas detecting elementfaces the gas exposure portion and an optical density detection portionof the gas detecting element faces said optical density measuringportion.
 7. A gas detecting device according to claim 6, wherein saidoptical density detection portion and said gas detecting element areconstituted so as to maintain airtightness.